1. Field of the Invention
The present invention relates to a V-type two-cylinder engine suitable for being mounted on an all terrain vehicle (referred to as ATV), and a straddle-type four wheel all terrain vehicle on which the engine is mounted.
2. Description of the Related Art
Some motor cycles include V-type two cylinder engines mounted thereon. The V-type two cylinder engine has an advantage over other type engines having the same engine displacement in that a width (dimension in a longitudinal direction of a crank shaft) of the engine can be reduced because cylinders can be placed such that they are partially overlapped seen in a front view (seen from a direction orthogonal to the crank shaft). For this reason, the V-type two-cylinder engine is suitable for a straddle-type vehicle.
In the prior art, there has been proposed an all terrain vehicle on which the V-type two-cylinder engine is mounted. This all terrain vehicle has an engine in which a carburetor is provided between forward and rearward cylinders arranged in V shape and an air cleaner is provided above the carburetor and covered with a cover situated above (see Japanese Laid Open Publication No. Hei. 1-172083). However, with this configuration, the following technical problems arise.
(a) When two carburetors are provided according to placement of respective cylinders to obtain suitable performance for various operating conditions of the all terrain vehicle, it is impossible to place them on an axis parallel to the crank shaft like an inline-shaped engine, because these cylinders are arranged in V shape and placed as having positional difference between them in a direction of the crank shaft. Accordingly, each of the carburetors is independently placed for each of the cylinders at an appropriate position adapted to a position of each of the cylinders.
In this case, it is necessary to set up a throttle lever, a choke lever, and the like for each of the carburetors and provide fixing members having high rigidity and complex shapes for fixing the carburetors at predetermined positions, fixing members for the air cleaner, and a cooperating mechanism for cooperating levers of the carburetors. In this case, the entire intake equipment including the two carburetors has a complex structure and the number of parts is increased. As a consequence, man-hour of assemblies is increased and hence, a manufacturing cost is increased. Japanese Utility Model Application Publication No. Sho 60-66862 discloses such a prior art.
When the V-type two cylinder engine is configured such that the carburetors are placed in parallel on an axis orthogonal to the crank shaft, a distance between an intake port of one cylinder and a venturi bore (exit of fuel-air mixture of an carburetor) of the corresponding carburetor differs from a distance between an intake port of the other cylinder and a venturi bore of the corresponding carburetor. Accordingly, two intake manifolds each connecting the intake port and the venturi bore have different lengths and are curved at the middle thereof. Such a configuration is less preferable to engine performance and a manufacturing cost of the intake manifolds is high because of complex shapes.
(b) Since the all terrain vehicle is limited in space, the air cleaner might be placed immediately above the carburetors such that it covers the carburetors. In case of the all terrain vehicle traveling in atmosphere in which water or mud is flying in all directions, the air cleaner or the like requires any measures to prevent attachment (adherence) of the mud or water to a filter of the air cleaner.
(c) While an air bent tube for making the interior of the carburetor communicate with atmosphere and guiding an opening thereof to a desirable position might be extended below the air cleaner, it is required that a predetermined length of the air bent tube be horizontally placed below the air cleaner. With such a configuration, fuel is accumulated in the horizontally extended portion of the air vent tube and a primary function of the air bent tube for making the interior of the carburetor communicate with atmosphere is impeded. Further, the position of the opening of the air vent tube is restricted by parts around the carburetors.
The present invention has been developed for the purpose of obviating the above-described problems, and a first object of the present invention is to provide a V-type two cylinder engine suitable for a straddle-type four wheel all terrain vehicle that includes a compact intake equipment having a simple configuration and being manufactured at a low cost, in which a distance between an intake port of one cylinder and a venturi bore of the corresponding carburetor is equal to a distance between an intake port of the other cylinder and a venturi bore of the corresponding carburetor and connecting members and the like for connecting these parts are less curved.
A second object of the present invention is to provide a V-type two cylinder engine suitable for a straddle-type four wheel all terrain vehicle, comprising an air cleaner with improved maintainability and compactness that is capable of reducing attachment (adherence) of water, mud or the like contained in introduced air to a filter, with a compact configuration.
A third object of the present invention is to provide a V-type two cylinder engine suitable for a straddle-type four wheel all terrain vehicle comprising an air vent system of carburetors that is capable of preventing fuel from being accumulated in an air vent tube with a simple configuration and freely setting a position at which the air vent tube is opened in atmosphere and has a superior external design appearance when an air cleaner is placed above the carburetors.
A fourth object of the present invention is to provide a straddle-type four wheel all terrain vehicle on which the above-described V-type two-cylinder engine is mounted.
To achieve the first object of the present invention, there is provided a V-type two cylinder engine of the present invention comprising: cylinders arranged forward and rearward such that they are inclined in V shape; a downdraft carburetor unit placed between the cylinders and including twin venturi bores provided for the respective cylinders and an air vent system making the interior of carburetors communicate with atmosphere; intake manifolds each connecting a venturi bore of each of the carburetors to an intake port of a corresponding cylinder; and an air cleaner placed above the carburetors such that it covers the carburetors, wherein the carburetor unit is placed obliquely seen in a plan view according to positional difference between the cylinders in a direction of a crank shaft of the engine such that the venturi bore of each of the carburetors is closer to the intake port formed in a corresponding cylinder.
In the V-type two cylinder engine so configured, a distance between an intake port of one cylinder and a venturi bore (opening through which fuel-air mixture is supplied from the carburetor to the cylinder) of the corresponding carburetor can be made equal to a distance between an intake port of the other cylinder and a venturi bore of the corresponding carburetor and these distances can be made short. Besides, the intake manifolds are short and less curved. Therefore, this configuration is preferable to improvement of engine performance. Further, the carburetor unit, the air cleaner, and the like are efficiently placed in a space above the engine, which has been conventionally a dead space, and a distance from the air cleaner to the cylinder is short and connecting members for connecting these parts are less curved. Such a configuration, in addition to placement of the carburetors, realizes an efficient and compact intake equipment and a V-type two cylinder engine suitable for a straddle-type four wheel all terrain vehicle.
It is preferable that the carburetor unit is placed obliquely such that the venturi bore of each of the carburetors is situated on an extended line of an intake passage formed in a corresponding cylinder. Thereby, the distance between the intake port of the cylinder and the corresponding carburetor can be made equal to the distance between the intake port of the other cylinder and the corresponding carburetor and these distances can be made short. Besides, the connecting members and the like for connecting these parts are less curved.
It is preferable that the venturi bore of each of the carburetors is placed substantially on a line extending in a direction orthogonal to the crank shaft through the intake port of a corresponding cylinder.
To achieve the second object of the invention, the air cleaner of V-type two cylinder engine comprises: a body having an intake hole provided in a side face thereof and connecting holes connected to the carburetors; an intake duct connected to an inlet of the intake hole; a guide passage provided inside of the body and at an outlet of the intake hole for guiding air flowing through the intake hole upward; and a filter placed inside of the body such that it separates a portion downstream from the guide passage into a dirty area continuous with the guide passage and a clean area in which the connecting holes are opened, for filtering air flowing through the guide passage toward the connecting holes.
Such a configuration provides a V-type two cylinder engine comprising the air cleaner in which air flowing through the intake hole formed in the side face thereof collides with a wall face of the guide passage that is opposite to the outlet of the intake hole, and the water, mud or the like contained in the air is attached to the wall face of the guide passage or dropped downward.
It is preferable that the intake hole is provided in a lower end portion of the side face of the body, the intake duct extends obliquely and downward from a tip end thereof and reaches the inlet of the intake hole, the filter is provided in a substantially horizontal direction to allow air flowing through the guide passage to pass through the filter from above and move downward toward the connecting holes, thereby forming a dirty area above the filter and a clean area below the filter with a wall disposed between the guide passage and the clean area, and the connecting holes are provided in a bottom face of the clean area of the body.
With such a configuration, the air cleaner adapted to move the introduced air upward can be made as low as possible. In addition, an effective area of the filter can be made larger without a substantial increase in the height of the air cleaner. Further, the air passing through the filter moves downward and clean air can be efficiently introduced to downdraft carburetors.
It is preferable that the intake duct has a passage section area gradually increased from the tip end thereof to the base end thereof. Since the flow velocity of the air introduced through the tip end of the intake duct is gradually reduced, the water, mud or the like can be efficiently removed when the air collides with the wall face of the guide passage.
To achieve the third object, in the V-type two cylinder engine, each of the carburetors of the carburetor unit comprises a float chamber and an air vent passage making the float chamber communicate with atmosphere, and the air vent passage is guided to inside of the body of the air cleaner, where the air vent passage slopes up to a highest point from which the air vent passage slopes down.
The air vent passage does not include a long horizontal portion. Therefore, if the fuel goes into the air vent passage from the float chamber of the carburetor during traveling of the vehicle, gravity applied on the fuel in the air vent passage cause the fuel to return to the float chamber. This prevents accumulation and clogging of the fuel in the air vent passage. As a consequence, a pressure in the float chamber of the carburetor is stabilized. Moreover, the opening of the air vent passage can be provided at a suitable position by utilizing the space in the air cleaner without being restricted by the carburetors or parts around the carburetors and such a configuration has an excellent external design appearance.
It is preferable that the air vent passage comprises an inner air passage making the float chamber of the carburetor communicate with atmosphere and an outer air passage extended from the inner air passage, and the outer air passage comprises: a first outer air passage extending from an outlet of the inner air passage through inside of the air cleaner to an exit portion provided in the air cleaner; and a second outer air passage extended from the exit portion of the air cleaner, and a tip end of the second outer passage is opened in atmosphere.
Thereby, the opening of the air vent passage can be easily provided at a suitable position with a simple configuration.
It is preferable that the second outer air passage extends downward from the exit portion provided in the air cleaner, and an intermediate air vent hole is provided in the exit portion so as to open a base end of the second outer air passage opened in atmosphere.
With such a configuration, the air vent system is suitable for the straddle-type four wheel all terrain vehicle traveling in water or on rough terrain with much dust.
To achieve the fourth object, there is provided a straddle-type four wheel all terrain vehicle comprising: a straddle-type seat; a steering handle provided forward of the seat; a top cover covering an upper portion of a vehicle body, through which a rotating shaft of the steering handle penetrates; and a V-type two cylinder engine mounted below the seat and the handle an between the seat and the handle, wherein the V-type two cylinder engine comprises: cylinders arranged forward and rearward such that they are inclined in V shape; a downdraft carburetor unit placed between the cylinders and including twin venturi bores provided for the respective cylinders and an air vent system making interior of carburetors communicate with atmosphere; intake manifolds each connecting a venturi bore of each of the carburetors to an intake port of a corresponding cylinder; and an air cleaner placed above the carburetors such that it covers the carburetors, wherein the carburetor unit is placed obliquely seen in a plan view according to positional difference between the cylinders in a direction of a crank shaft of the engine such that the venturi bore of each of the carburetors is closer to the intake port formed in a corresponding cylinder.
According to the straddle-type four wheel all terrain vehicle so configured, the V-type two cylinder engine with high performance can be compactly mounted in a space below the straddle-type seat and the steering handle situated forward of the seat and between the seat and the handle, and the vehicle is easy for the rider to straddle in a width direction thereof.
It is preferable that in the straddle-type four wheel all terrain vehicle, a relay chamber is formed inside of the top cover, the relay chamber being surrounded by a separating wall and having a clearance between a rotating shaft of the handle and the top cover, for introducing fresh area, and an opening of the air cleaner for introducing fresh area is opened inside of the relay chamber.
With such a configuration, since the opening of the air cleaner for introducing fresh area can be provided in an upper and central portion of the vehicle body and is covered with the top cover, the water or mud and the like hardly enters the opening. Besides, the opening can be simply structured and formed around the rotating shaft of the handle and just before a rider. Therefore, if the opening is clogged with foreign substances, they can be found immediately and removed.
It is preferable that in the straddle-type all terrain four wheel vehicle, the top cover has a swelled portion which is raised upward around the rotating shaft and the relay chamber is formed inside of the swelled portion. With this configuration, the relay chamber is made easily at a high position of the vehicle.
Also, it is preferable that in the straddle-type all terrain vehicle, the air vent system of the carburetors includes an air vent passage connecting carburetors and atmosphere, and the air vent passage has a portion passing through inside of the air cleaner and a tip end opened in atmosphere.
Thereby, the air vent passage can be placed without being restricted by the carburetors and its surrounding parts and its external design appearance can be improved.
Preferably, in the straddle-type four wheel all terrain vehicle, the air cleaner comprises: a body having an intake hole provided in a side face thereof and connecting holes connected to the carburetors; an intake duct connected to an inlet of the intake hole; a guide passage provided inside of the body and at an outlet of the intake hole for guiding air flowing through the intake hole upward; and a filter placed inside of the body such that it separates a portion downstream from the guide passage into a dirty area continuous with the guide passage and a clean area in which the connecting holes are opened, for filtering air flowing through the guide passage to the connecting holes, wherein the intake duct has a tip end opened inside of the top cover and extends obliquely and downward to reach an inlet of the intake hole, the filter is provided in a substantially horizontal direction to allow air flowing through the guide passage to pass through the filter from above and move downward toward the connecting holes, thereby forming a dirty area above the filter and a clean area below the filter with a wall disposed between the guide passage and the clean area, and the connecting holes are provided in a bottom face of the clean area of the body.
With such a configuration, it is possible to provide the straddle-type all terrain vehicle comprising the V-type two cylinder engine mounted thereon that is capable of introducing fresh area containing less dust into the air cleaner and efficiently removing the dust in the air cleaner to supply clean air to the carburetors. Further, the compact and high-performance straddle-type four wheel all terrain vehicle is obtained.
Preferably, in the straddle-type four wheel all terrain vehicle, the air cleaner comprises: a body having an intake hole provided in a side face thereof and connecting holes connected to the carburetors; an intake duct connected to an inlet of the intake hole; a guide passage provided inside of the body and at an outlet of the intake hole for guiding air flowing through the intake hole upward; and a filter placed inside of the body such that it separates a portion downstream from the guide passage into a dirty area continuous with the guide passage and a clean area in which the connecting holes are opened, for filtering air flowing through the guide passage to the connecting holes, wherein the intake duct has a tip end opened inside of the relay chamber and extends obliquely and downward to reach an inlet of the intake hole, the filter is provided in a substantially horizontal direction to allow air flowing through the guide passage to pass the filter from above and move downward toward the connecting holes, thereby forming a dirty area above the filter and a clean area below the filter with a wall disposed between the guide passage and the clean area, and the connecting holes are provided in a bottom face of the clean area of the body.
With such a configuration, it is possible to provide the straddle-type four wheel all terrain vehicle comprising the V-type two cylinder engine mounted thereon that is capable of introducing fresh area containing less dust into the air cleaner and efficiently removing the dust to supply clean air to the carburetors when traveling on rough terrain. Further, the compact and high-performance straddle-type four wheel all terrain vehicle is obtained.
These objects, as well as other objects, features and advantages of the invention will become more apparent to those skilled in the art from the following description with reference to the accompanying drawings.